R help - Feb 2004 - problem with unlist

Hello, I try to compute means,sd,n from a variable y according to some 
categoricals g1,g2... I wrote the following function:
msd<-function(y,...) {
    print(match.call())
    funy<-function(x) list(mean(x,na.rm=T),sd(x,na.rm=T),table(is.na(x))[1])
    gg <- list(...)
    aa<-by(y,gg,funy)
    bb<-matrix(unlist(aa),nrow=3)
    bb
}
this works OK so far there is no empty cell in the crosstab, if there 
is, the unlist statement just run over it and I do not know which cell 
is missing, any attempt to label the columns in matrix bb then fail.
Can somebody suggest a method to retrive the list names from aa to label 
the columns of the matrix bb?
Thanks for any help
Heberto Ghezzo
McGill University
Montreal Canada

Why not just do:

tapply(y, list(g1, g2, ...), function(x) c(mean=mean(x, na.rm=TRUE),
sd=sd(x, na.rm=TRUE), n=sum(!is.na(x))))

??

Andy
> From: r.ghezzo
> 
> Hello, I try to compute means,sd,n from a variable y 
> according to some 
> categoricals g1,g2... I wrote the following function:
> msd<-function(y,...) {
>     print(match.call())
>     funy<-function(x) 
> list(mean(x,na.rm=T),sd(x,na.rm=T),table(is.na(x))[1])
>     gg <- list(...)
>     aa<-by(y,gg,funy)
>     bb<-matrix(unlist(aa),nrow=3)
>     bb
> }
> this works OK so far there is no empty cell in the crosstab, if there 
> is, the unlist statement just run over it and I do not know 
> which cell 
> is missing, any attempt to label the columns in matrix bb then fail.
> Can somebody suggest a method to retrive the list names from 
> aa to label 
> the columns of the matrix bb?
> Thanks for any help
> Heberto Ghezzo
> McGill University
> Montreal Canada
> 
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